The present invention relates generally to inking systems for printing machines, and more particularly, to inking systems in which ink or lacquer can be directed through a roller train leading to a plate or form cylinder.
A printing machine with a vibrating inking unit is known from DE 37 06 602 A1. Here, an ink fountain roller is associated with an ink fountain having a metering system for the printing ink, as is known from DE 27 11 553 A1. For printing machines with a vibrating inking unit, the printing ink is periodically removed in strips from an ink fountain roller by back and forth pendulate motion of an ink vibrating roller and fed to an inking unit roller of the subsequent roller train. Limited by the different rotational speeds of the ink fountain roller and the inking unit roller, vibrating inking units have the problem that the inking vibrating roller is delayed or accelerated with each strike (contact) with the ink fountain roller or the inking unit roller. With such striking or lifting of the vibrating roller, there is non-uniform ink guidance during transport of the printing ink, in connection with an up-and-down ink separation in the contact zone of the rollers, as well on the ink fountain roller or on the inking unit roller, which adversely affects the printing quality. Due to the ink separation of the printing inks between the ink fountain roller and the ink vibrating roller, as well as between the ink vibrating roller and the subsequent inking unit roller, uneven surface structures are formed for the remaining ink on the roller surfaces, which further leads to reduced printing quality on the material.
From DE 38 04 204 A1, a printing machine inking unit with a film roller is known. Such a film roller is designed for the ink transport across a film gap (first contact zone) in contact with the ink fountain roller, as well as in a second contact zone with the subsequent inking unit roller of a subsequent roller train, so that a continuous ink transport of printing ink between the ink fountain roller and the inking unit roller of the roller train can be effected. In addition, an intermediate roller is arranged in contact with the film roller and a doctor blade roller is arranged after this intermediate roller. In contact with the doctor blade roller is an adjustable doctor blade, and the doctor blade can be set or adjusted depending on the subject or at intervals on the doctor blade roller. The printing ink removed by the doctor blade roller is then led back into the ink fountain. This film inking unit is used for minimizing the amount of ink by removing a portion of ink from an inking unit and is relatively expensive due to the use of additional rollers (intermediate roller, doctor blade roller). In the contact zones of the ink fountain roller and film roller and the film roller and subsequent inking unit roller, there occurs, analogous to the above described vibrating inking unit, an ink separation of the printing ink per contact zone so that also for film inking units, which results in uneven surface structures being formed in the ink on the roller surfaces which leads to reduced printing quality on the printing material.
Furthermore, from DE 196 09 946 A1 there is known a printing machine with an applicator for inking a roller of an inking unit. The applicator consists of a storage container with ink or lacquer or a comparable medium, which has an associated metering roller. The metering roller is in friction contact with a drivable roller for ink transfer and thus forms a contact zone in which ink or lacquer separation occurs.
According to DE 42 41 809 A1, a printing machine with a device for the inking of rollers is known, which leads ink from a storage container under compressed air according to zones in the axial direction of the rollers onto their outer surfaces. In this way, there is no contact on the side of the device with the outer surface of the associated rollers to be inked. The zone-wise deposited ink forms a different amount of ink on the outer surface of the inked roller, which exhibits an uneven surface structure for the ink.
Such an uneven surface structure for the ink on the outer surface of a roller results from pulling off of the ink, e.g., for ink emerging from a storage container and striking an outer surface, or after an ink separation process (division of the ink layer) in the contact zone of two rollers or the contact zone of a roller with a stripping system, e.g., an ink metering system.
From DE 199 38 301 A1 there is known an inking unit for a printing machine for the uniform application of ink. Starting from the fact that there is tension at the roller gap formed by two rollers, there results a non-uniform ink transfer. Such tension influences, e.g., the line pressure in the roller gap of two rollers, and this different line pressure effects, e.g., a non-uniform ink transfer, which appears on the printing material as an ink film that has been applied non-uniformly. For improving the ink transfer, there is at least one smoothing element associated with an inking unit roller that removes shearing forces of the ink. Preferably, the smoothing element is associated with an ink applying roller and/or an ink friction roller adjacent to the plate cylinder.
It is an object of the present invention to provide a inking system for ink or lacquers in a printing machine which is relatively economical in construction and adapted for uniform, stable ink or lacquer guidance on one or more roller surfaces for improved printing quality.
It has been found that on the outer surface of an ink or lacquer guiding roller, after the pulling off (shearing) of ink (or lacquer) in a contact zone, the ink/lacquer distribution is not uniform across the roller width. On the roller there is an uneven surface structure of ink (lacquer), which is characterized by ink peaks or ink cones and ink valleys (or lacquer peaks, lacquer cones, lacquer valleys) on the outer surface of an ink-guiding roller.
For example, for an ink fountain roller, after the ink separation (splitting of ink layer) in a contact zone with another roller, e.g., a vibrating or film roller, through pulling off of ink/lacquer, particularly for thread-like pulling off, the ink/lacquer distribution is not uniform across the roller width, but instead there is an uneven surface structure of the remaining ink (or the remaining lacquer) on the outer surface of the ink fountain roller. This also applies to ink zones generated within an ink metering system having ink metering elements where layer thickness is defined in zones, because in that case a pulling off of ink or lacquer also occurs as a consequence of the shearing forces separating the ink (lacquer).
A first advantage of the present invention is based on the fact that for an uneven surface structure (peaks, cones, and valleys) of ink (lacquer) which results from prior pulling off of ink (lacquer), at least one ink-guiding (or lacquer-guiding) roller is assigned to at least one plating device at its periphery. The plating device effects a shape change (plastic shaping) of the ink peaks or ink cones and ink valleys (or lacquer peaks, lacquer cones, lacquer valleys) within the surface structure of the ink (or lacquer). The shape change represents a micro-conversion of the surface structure of the ink (lacquer). For such a shape change of the ink (lacquer), the ink peaks or ink cones (lacquer peaks, lacquer cons) slide into the ink valleys (lacquer valleys), i.e., smoothing processes are performed within the ink layer on the ink texture (lacquer texture), which effect plastic shaping so that an approximately even surface structure can be achieved with a defined layer thickness. The plastic shaping by the plating device is advantageous because the ink or the lacquer is not exposed to a shearing effect (shearing or dispersion effect). A shearing effect leads, in turn, to undesired pulling off of ink or lacquer and thus to uneven surface structure.
The relatively even surface structure of ink (or lacquer) achieved by the plating device has the effect that ink/lacquer density variations can be noticeably reduced on the printing material so that the printing/gloss or reflective quality is noticeably improved. As a result, there is an even surface structure of the ink or remaining ink or lacquer on the outer surface of the corresponding roller across the roller width before the roller comes in contact with a subsequent contact zone (e.g., a gap position). With such a plating device, this uneven surface structure of the ink or remaining ink or lacquer is clearly leveled in an advantageous way on the associated roller, e.g., the ink fountain roller, so that a uniform surface structure of the ink or remaining ink or lacquer can be achieved for a uniform, stable ink/lacquer guidance in the roller train.
The use of a plating device, particularly on an ink fountain roller, is advantageous because a clearly reduced amount of printing ink in the metering gap (gap between ink metering system, e.g., ink valves, and ink fountain roller) is passed through the metering gap. It is likewise an advantage that particularly the parameters changing during the printing process, such as printing speed, temperature, ink amount, hydrodynamic pressure in the ink fountain, as well as the viscosity of the printing ink or the lacquer, are noticeably reduced as possible interference variables by the use of a plating device according to the invention.
Another advantage is that the plating device according to the invention is not limited to one ink fountain roller. The arrangement of plating devices can also be realized for other ink-guiding (including lacquer-guiding) rollers of an inking unit. Here, preferably at least one plating device is assigned to each roller. Alternatively, several plating devices can also be arranged for one roller.
It is likewise advantageous if the surfaces of the ink or remaining ink or lacquer, which are leveled uniformly by the plating device, lead to uniform ratios for the subsequent ink/lacquer separation (in the ink metering system) in the ink fountain or to uniform separation ratios between adjacent rollers (contact zones) themselves, which noticeably improves the print quality. With the leveling of ink or lacquer on the outer surface of a roller, a homogenous ink layer is created, which can be more easily metered. In this way, a smaller distance of the ink metering elements of the ink metering system to the roller for the same ink thickness (lacquer thickness) can be realized and a continuous ink flow achieved.
Furthermore, the inking unit according to the invention reduces by a considerable extent the interference of the ink flow through the independently controlled rpms and, if necessary, the direction of rotation of the roller, e.g., of the film roller, which can achieve better adaptation of the ink flow to the printing speed.
Furthermore, according to the geometry of the roller train in the inking unit, there is the possibility of reducing the number of inking rollers. Therefore, a uniform surface structure of the remaining ink or the remaining lacquer on a roller can be achieved with fewer gap points in order to achieve a defined layer thickness of the ink film on the plate cylinder. In this way, the roller train also can be shortened.
The plating device is used for creating a relatively even surface structure on the outer surface of a corresponding ink or lacquer-guiding roller. In the region of the plating device, a pulling off/shearing of ink or lacquer is to be prevented at the outer surface of the corresponding roller, because otherwise this leads to uneven surface structures. The configuration of the plating device is not limited to one or more mechanical plating device(s) with one or more plating element(s). For example, for achieving an even surface structure, an air doctor blade that introduces compressed or blown air onto the outer surface of the ink/lacquer guiding roller or an ultrasonic system directed onto the ink can be used in order to achieve plastic shaping.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: